I ran limesurvey 3.6.2 behind a reverse proxy with ssl offload (haproxy). It ran for around 3 months (not really sure, the version would be a good indicator).
I had to modify the SSL certificate on the reverse proxy (I was not able to connect to the json api) and now the system stopped working. I had not touched the limesurvey installation at all as this was only related to the certificate.

Configuration as follows:
Client using SSL -> Router -> reverse proxy (haproxy) terminating the ssl connection and sending 301 to indicate that there is no http any more -> limesurvey server (without ssl)

I do not know why this happens right now but I think that the client connects the reverse proxy, is redirected to https and receives a redirect to http from limesurvey server -> endless loop

In my config.php I have (obscured domain name):

returnarray('components'=>array('db'=>***,'log'=>array('routes'=>array('fileError'=>array('class'=>'CFileLogRoute','levels'=>'warning, error','except'=>'exception.CHttpException.404',),),),// Enforce a certain URL base 'request'=>array('hostInfo'=>'https://domain/'),// Uncomment the following line if you need table-based sessions// 'session' => array (// 'class' => 'application.core.web.DbHttpSession',// 'connectionID' => 'db',// 'sessionTableName' => '{{sessions}}',// ),'urlManager'=>array('urlFormat'=>'path','rules'=>array(// You can add your own rules here),'showScriptName'=>true,),),// For security issue : it's better to set runtimePath out of web access// Directory must be readable and writable by the webuser// 'runtimePath'=>'/var/limesurvey/runtime/'// Use the following config variable to set modified optional settings copied from config-defaults.php'config'=>array(// debug: Set this to 1 if you are looking for errors. If you still get no errors after enabling this// then please check your error-logs - either in your hosting provider admin panel or in some /logs directory// on your webspace.// LimeSurvey developers: Set this to 2 to additionally display STRICT PHP error messages and get full access to standard templates'debug'=>0,'debugsql'=>0,// Set this to 1 to enanble sql logging, only active when debug = 2'enableLdap'=>true,// Update default LimeSurvey config here'sitename'=>'Our LimeSurvey','RPCInterface'=>'json',//'publicurl' => 'https://domain/',//'homeurl' => 'https://domain/admin',));

1. Can you access LimeSurvey via browser as a user/login and e.g. create a survey.
If not, what is the error message in the browser. Test a few.
2. What webserver is used?
3. What does "modify the certificate" means?

I still try to understand the purpose of the whole setup. You want to take load of the limesurvey server with putting TLS transport encryption on a reverse proxy.

1. no , currently I cannot access LimeSurvey via browser. The message says: "Redirection error - The site redirects the request in a manner that cannot be finished" (translated from german).
2. Apache2 2.4
3. Everything worked with the reverse proxy and ssl but when I tried to access the remote api via the mentioned JSON RPC client I got several error messages which indicates that there is a problem with the certificates (return error value: 21 cannot check first certificate). To resolve the problem I had to integrate the intermediate certificate into the pem file on the reverse proxy. Before this I had a working LimeSurvey where the last modification was to enable the remote API.
The reason for this setup is that I have only one official IP but want to serve several sites and services (Moodle, Mahara, Nextcloud, QueXF, BigBlueButton, ...). Therefore I put them on different servers and set a reverse proxy in front to distribute the traffic. Additionally I can add a new server or service, add it to the reverse proxy and get a tested SSL implementation.
4. Because I cannot access the site at the moment I can only look into the config file and there I see 'neither'.

Assistance on LimeSurvey forum and LimeSurvey core development are on my free time.
I'm not a LimeSurvey GmbH member,
professional service on demand
(or search sondages pro).
An error happen ? Before make a new topic : remind the
Debug mode
.

Assistance on LimeSurvey forum and LimeSurvey core development are on my free time.
I'm not a LimeSurvey GmbH member,
professional service on demand
(or search sondages pro).
An error happen ? Before make a new topic : remind the
Debug mode
.

Here , i don't know what cookieParam you need to keep the session. Only sysadmin can answer to this.

Assistance on LimeSurvey forum and LimeSurvey core development are on my free time.
I'm not a LimeSurvey GmbH member,
professional service on demand
(or search sondages pro).
An error happen ? Before make a new topic : remind the
Debug mode
.

as I am the administrator of these servers I am afraid that I am the only one for this position
I am not sure if the cookies are the problem at the moment. I have no tool to check the real communication but I think that LimeSurvey get the request as http, forces https, gets the "new" request once again as http...

It would be great if LimeSurvey could just answer the request without modifying the protocol...

cadguru wrote: It would be great if LimeSurvey could just answer the request without modifying the protocol...

This is the reason i ask you to set neither …

With neither : receive http, send http … receive https : send https.

Maybe your proxy update the protocol …

Assistance on LimeSurvey forum and LimeSurvey core development are on my free time.
I'm not a LimeSurvey GmbH member,
professional service on demand
(or search sondages pro).
An error happen ? Before make a new topic : remind the
Debug mode
.

Assistance on LimeSurvey forum and LimeSurvey core development are on my free time.
I'm not a LimeSurvey GmbH member,
professional service on demand
(or search sondages pro).
An error happen ? Before make a new topic : remind the
Debug mode
.

By default : LimeSurvey work out of the box , but your config need some specific settings.

Assistance on LimeSurvey forum and LimeSurvey core development are on my free time.
I'm not a LimeSurvey GmbH member,
professional service on demand
(or search sondages pro).
An error happen ? Before make a new topic : remind the
Debug mode
.